The present invention relates to a sewing machine for forming running-stitch seams.
Sewing machines for forming a seam with a so-called running stitch are known; said seam is formed with a single thread of preset length, known as draw, and is composed of stitches that are alternately visible on either side of the fabric being sewn.
A machine of this kind is disclosed in U.S. Pat. No. 4,122,787 and is substantially composed of a needle that has a substantially vertical axis and is provided, proximate to its tip, with an open eye and is orientated so that its axis is substantially perpendicular to a supporting surface on which the item being sewn is deposited.
The needle is actuatable with a reciprocating motion along its axis in order to pass cyclically through the item deposited on the supporting surface, carrying in each instance below and above the supporting surface a loop of thread of the draw used for the seam. One end of the draw is clamped beforehand above the item being sewn, while the other end of the draw is left loose.
Below the supporting surface there is a thread take-up wheel, which is arranged on a plane that is substantially parallel to the axis of the needle and is orientated so that its axis is substantially perpendicular to the axis of the needle. Said wheel is composed of a fixed part, in which there is a magazine for the taken-up thread, and of a rotatable part, which can be actuated with a rotary motion about its own axis. The rotatable part of the wheel is mounted coaxially on an actuation shaft, which can be actuated with a rotary motion about its own axis synchronously with the movement of the needle, and has, in a peripheral region, a looper or lower looper which, as a consequence of the rotation of the rotatable part of the wheel and of the movement of the needle, engages the loop of thread carried below the supporting surface by the needle and takes up the portion of thread that lies between the looper and the free end of the draw, making it pass inside the magazine provided in the fixed part of the wheel.
The machine is completed by thread handling means, which are located below the supporting surface, and by another looper, or upper looper, which is arranged above the supporting surface laterally to the needle and is meant to engage the loop of thread carried by the needle above the supporting surface and retain it while the thread is loaded by the lower looper in the magazine formed in the fixed part of the wheel.
The thread handling means comprise means for moving the portion of thread that lies below the supporting surface between the item being sewn and the thread magazine formed in the wheel away from the path of the needle in order to prevent said needle from engaging it during specific steps of the forming of the stitches.
The thread handling means also comprise means for moving said portion of thread toward the path of the needle, so as to place the thread against the shank of the needle above the eye, while said eye is located below the item being sewn, so that the subsequent upward motion of the needle causes the eye of the needle to engage the thread and form a loop of thread that is carried above the item being sewn.
The thread handling means further comprise a clamp, which is arranged proximate to the inlet of the magazine formed in the wheel and is meant to block the thread in order to prevent it from being extracted from the take-up magazine while the thread movement means move it away and then toward the path of the needle.
In order to prevent interference, during the loading of one part of the thread inside the magazine formed in the wheel and the simultaneous extraction of another part of thread from the same magazine, between the two thread parts that move in mutually opposite directions, there are appropriate separator means that mutually space said two thread parts.
The use of a clamp, which acts cyclically on the thread by clamping it and releasing it in order to allow it to slide for loading in the magazine and allow its subsequent extraction, has the problem of causing wear of the sewing thread, which can compromise the correct execution of the seam.
The aim of the present invention is to solve the above described problem, by providing a sewing machine for forming running-stitch seams that can operate correctly even without clamping the thread below the supporting surface, thus avoiding deterioration of the sewing thread.
Within this aim, an object of the invention is to provide a sewing machine in which the thread handling elements arranged below the supporting surface are structurally simpler than those of known types of running-stitch sewing machine.
Another object of the invention is to provide a sewing machine that ensures highly regular execution of stitches.
Another object of the invention is to provide a sewing machine for forming running-stitch seams that ensures a substantially uniform tension of the thread during the formation of the stitches.
This aim and these and other objects that will become better apparent hereinafter are achieved by a sewing machine for forming running-stitch seams, comprising a needle which has, proximate to its tip, an open eye and is orientated so that its axis is substantially perpendicular to a surface for supporting the item being sewn, and means for clamping one end of a draw of thread which are arranged above said supporting surface; said needle being actuatable with a reciprocating motion along its own axis in order to pass cyclically through the item being sewn and said supporting surface, carrying in each instance below and above said supporting surface a loop of thread of said draw in which one end is clamped at the beginning of the seam by said clamping means and the other end is free; a thread take-up wheel being provided below said supporting surface, being arranged on a plane that is substantially parallel to the axis of said needle, and being orientated so that its axis is substantially perpendicular to the axis of said needle; said wheel being composed of a fixed part, in which there is a magazine for the taken-up thread, and of a rotatable part, which can be rotationally actuated about its own axis; said rotatable part of the wheel being mounted coaxially on an actuation shaft that can be rotationally actuated about its own axis synchronously with the movement of said needle and supporting a lower looper that can engage the loop of thread carried below said supporting surface by said needle in order to take up, below said supporting surface, the portion of draw that lies between said needle and the free end of the draw and load it into said magazine formed in the fixed part of the thread take-up wheel; means for handling the thread being provided below said supporting surface and comprising means for moving the portion of thread that lies between the item being sewn and said thread magazine away from the path of the needle, means being also provided for moving said portion of thread toward the path of the needle, means being further provided for separating the two parts of the loop of thread engaged by said lower looper, characterized in that said means for moving the thread toward the path of the needle comprise a fork element and in that said separator means comprise a separator element that is arranged proximate to said fork element and can move so as to open the fork of said fork element in order to allow the entry in the fork of a segment, located below said supporting surface, of the part of the loop of thread that lies, in each instance, between said lower looper and said end of the draw clamped at the beginning of the seam and close the fork of said fork element in order to retain inside said fork said segment of the part of the loop of thread.